148 



GEOLOGY OF THE SECOND DISTRICT. 



47. 



The folds or contortions represented in the figure are of course somewhat distorted, but 

 they are the supposed forms which the strata are made to assume when subjected to lateral 

 pressure ; rising up on one side in a gradual slope, while on the other the descent is sudden 

 and rapid. Folds and plications on a small scale, of the same character, exist at numerous 

 places in the disturbed shales of Lorrain, as well as in the slates of the Taconic system, in 

 . which all the curvatures are preserved. When, however, we look for them in our mountain 

 masses, it is rare to find them. If they exist at all, they must of course appear under the 

 modified form represented in fig. 48, in which the greater portions of the curvatures are 



48. 



broken off in the line b b, which will represent the present surface ; the long and gentle slope 

 on the eastern side would be still preserved, as well as the steeper and more abrupt one of the 

 western declivity. As it regards the difference in the steepness of the two sides of the moun- 

 tain ranges, the fact, as here stated, holds good in some places ; in others, it does not : it 

 depends upon the direction of the dip ; if that is to the east, the long and gentle slope is upon 

 the east side ; on the contrary, when the dip is to the west, the steep side looks to the east. 

 In this particular, the case is apparently precisely as in all others ; on the fractured side of 

 the strata we get steepness, a result which may, and often does result from an uplift accom- 

 panied with a fracture. The two diagrams which I have introduced to illustrate the theory of 

 curvatures, seem also to show the relative position which they preserve when thrown into 

 contortions ; they exhibit, too, the fact that strata may apparently dip beneath themselves, by 

 tracing those marked 1,2,3,4 respectively : it is, however, plain, as has been already stated 

 in the preceding pages, that where strata exist under this form, they cannot dip into the 

 mountain and form a part of the interior. The diagrams also are intended to show how the 

 lower rocks of New-York may be prolonged to the east, when being near the primary mass ; 

 and having besides been subjected to great pressure, their features and characters as fossili- 

 forous rocks arc concealed under their metamorphic dress. In this view, I have given my 



